The present invention relates to a heat exchanger element in general, and, particularly for solar collectors, comprising a metal plate welded centrally between its longitudinal edges to a metal tube, the width of the metal plate being greater than the cross sectional dimension of the tube and the metal plate being plastically deformed so as to increase its surface in regions between its longitudinal edges and its line of contact with the tube, while an undeformed region extends in the longitudinal direction of the tube between the deformation regions, and to a method for production of such a heat exchanger.
Solar collectors as an alternative source of energy for regions of abundant sunlight are becoming more and more important, particularly since they receive subsidies and incentives in many countries. Various solar collectors are known with a type of action based on the hot-house effect.
The core of all solar collectors of this type is the heat exchanger or heat exchange element which transfers the collected heat to a heat-carrier or heat exchanger fluid.
Heat exchangers have already been proposed which are made of a metal tube to which a metal plate is tangentially welded. The metal plate acts to increase the surface of the tube and transfers the collected heat energy to the tube and consequently to the heat exchanger fluid flowing within the tube. The optimization of a solar collector has as its purposes:
1. Optimization from a heat engineering standpoint; PA0 2. Optimization from a mechanical standpoint; and PA0 3. Optimization from a cost standpoint.
Since cost is the decisive factor, it must be attempted to use plates which are as thin as possible. However, they must also be stable in all directions, and must absorb the heat as best as possible and introduce it into the tube. If it is desired to use plates of a thickness of 0.25 mm and less, and particularly plates of a wall thickness from 0.15 to 0.18 mm, the plates can no longer be handled mechanically. They are too delicate to withstand subsequent assembly work without damage.
From U.S. Pat. No. 4,326,583 a heat exchanger for this purpose is known which consists of a metal tube with a metal plate welded to it. In order to prevent distortions due to the welding of the metal plate to the metal tube during or after the cooling of the weld seam, the regions of the metal plate on both sides of the weld seam which are not heated by the welding operation are provided with corrugations which run substantially transverse to the longitudinal direction of the tube. These corrugations are adapted to prevent the occurrence of distortions in the region of the weld seam very well and to increase the rigidity of the metal plate. However, they are still not completely satisfactory from a heat transfer standpoint.